Mice, transgenic for the S100A4 gene, which over express S100A4, show no phenotype, but when these mice are mated with mice bearing, as an expressed transgene, an activated oncogene, such as c-erbB-2, which produces benign mammary tumours, offspring which express both the onco-transgene and the S100A4 transgene, exhibit tumours which also metastasize to the lungs (Davies et al, 1996). The gene discussed is S100A4; the disease is neoplasm.